1. Field of the Invention
The coating or encapsulation of discrete particulate material by a variety of processes is well known. In particular, the art is aware of many variations in processes for coating particulate material by a fluidized bed technique.
The present invention finds utility for applying either a complete single coating or a double coating of a material to a particulate substance.
In the case of a single coating, encapsulation methods known heretofore do not always insure that the particles will have no adverse side effects during use.
The double coating process of the present invention is especially applicable to the coating of particles of highly reactive substances. Most particularly the process finds utility in the detergent bleach field wherein particulate fabric bleaching agents, such as potassium dichloroisocyanurate, sodium dichloroisocyanurate, and the hydrates thereof are employed in home laundering operations as a dry bleach product to be added separately to a washing machine on for use in admixture with particles of a detergent composition to form a commercially acceptable detergent - dry bleach combination. Because of their highly reactive nature the particles must not only be thoroughly and imperviously coated to avoid contact of the bleach particles with the detergent particles, but the coated particles must not attack textile materials or the dyes thereon under washing conditions. Although prior-art processes may provide thorough and uniform coatings impervious to potassium iodide solution, the coated particles of chlorine-releasing compounds suffer the defect that they attack the dye substances at the points of contact with the fabric and have been known to attack the fabric and make pinholes therein in a washing process wherein the coated bleach particles are placed directly on dry clothes.
2. The Prior Art
Art that may be considered in connection with the instant invention is represented by the patents listed below.